A woman who took isotretinoin during the fourth to eighth week of gestation delivers an infant with bilateral microtia, conotruncal cardiac defects, and thymic hypoplasia. The teratogen acts through which class of receptors to alter gene transcription?
- A Nuclear receptors forming RAR-RXR heterodimers ✓
- B Serine-threonine kinase membrane receptors
- C Seven-transmembrane G protein coupled receptors
- D Tyrosine kinase receptors of the EGFR family
Correct answer: A. Nuclear receptors forming RAR-RXR heterodimers
Explanation
Retinoic acid is a small lipophilic morphogen that enters the nucleus and binds retinoic acid receptors (RAR) paired with retinoid X receptors (RXR); the heterodimer binds retinoic acid response elements and regulates HOX and neural crest target genes. Excess RA induces apoptosis of cranial neural crest cells, producing the ear, cardiac outflow, and thymic defects seen here. The other receptor classes mediate peptide growth factors such as FGF, TGF-beta, and EGF, none of which bind isotretinoin.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.